A critical concern in the treatment of human malignancies is the emergence of tumor cells which are resistant to chemotherapy. Analysis of drug resistant human tumor cells in culture has shown that increased expression of the multidrug resistance (mdr1) gene is sufficient for the development of resistance to some hydrophobic chemotherapeutic agents. The long term objective of this research is to understand the molecular basis of increased expression of the mdr1 gene in human tumor cells. The proposed studies are designed to examine the regulation of mdr1 gene transcription. The goal of these studies is to determine the significance of utilization of distinct mdr1 promoter element, which have previously been shown in vivo and in vitro to be used differentially in expression of the mdr1 gene. This goal will be addressed by analyzing the transcriptional activity of the cloned mdr1 promoter region containing upstream and downstream promoters. The specific aims include: 1) determining the sequence and structure of both mdr1 promoters 2) examining the activity of the mdr1 upstream promoter 3) determining whether extracts from drug sensitive and resistant cells have differential activity for the mdr1 promoter 4) defining the sequence requirements for promoter activity. The transcriptional activity of the cloned mdr1 promoters will be analyzed in a cell-free transcription system. Experimentally manipulated genomic subclones of the promoter will be analyzed in extracts from drug sensitive and resistant cells to determine both the efficiency of the use of initiation sites and of the sequence requirements for promoter activity. These studies will provide an understanding of the role of mdr1 gene expression in the development of resistance to hydrophobic chemotherapeutic agents.